Escherichia Coli. Pathotypes and Principles of Pathogenesis

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See our disclaimer. Customer Reviews. Write a review. See any care plans, options and policies that may be associated with this product. Email address. Please enter a valid email address. Walmart Services. Get to Know Us. Customer Service. In The Spotlight. Shop Our Brands. All Rights Reserved. Light micrographs showing the distinctive patterns of adherence of enteroaggregative E. These patterns were responsible for the names of these pathotypes and were originally used to identify them in vitro. In , a Shiga toxin-producing derivative of an EAEC strain of serotype OH4, shot to prominence by causing a major foodborne outbreak of diarrhoea and HUS in Germany, with serious outcomes for human health and the international food trade Buchholz et al.

Few studies of diarrhoea today use the aggregative adherence phenotype to identify EAEC.

Are Escherichia coli Pathotypes Still Relevant in the Era of Whole-Genome Sequencing?

Instead most investigators target the pAA-borne genes, aatA and aggR that encode a transporter of a virulence protein and a virulence regulator, respectively , or the chromosomally-encoded aaiC gene which is also associated with virulence Table 1 ; Panchalingam et al. This issue is not trivial, because until it is resolved we will lack a clear definition of what really constitutes EAEC. Accordingly, few of these strains are considered DAEC, despite their phenotype. Although E.

This, and the fact that two prototypical DAEC strains failed to cause diarrhoea in volunteers who ingested up to 10 10 colony-forming units, casts doubt on the role of DAEC in diarrhoea, notwithstanding considerable evidence of the deleterious effects of these bacteria on intestinal epithelial cells in vitro reviewed in Servin, Instead they are thought to contribute to the development of Crohn's disease, which is a chronic inflammatory bowel disease. The aetiology of Crohn's disease is uncertain, but is likely to involve both host and environmental factors Alhagamhmad et al. AIEC strains are discernible from other varieties of E.

Escherichia coli pathogenesis

Thus, although AIEC are recovered more commonly from patients with Crohn's disease than from healthy people, it is unclear whether these bacteria contribute to the pathogenesis of Crohn's disease or are merely adapted to or enriched in intestinal tissue affected by this disease. The first complete genome sequence of an E. Since then many thousands of E. Nevertheless, from the available data we can glean that the size of the E. Each individual E. As more E.

The size of the core genome currently stands at fewer than genes and will to continue to diminish, albeit slowly, as more strains are sequenced.

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Genes that are not part of the core are referred to as the accessory genome. These include all of the genes that encode bacteriophage elements, virulence determinants and acquired resistance to antimicrobials.

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The E. All of the genes for E. Thus, every E. For these reasons, it is inevitable that new pathotypes of DEC will continue to emerge, either through novel assemblies of E. Apart from pathotype, individual strains of E. These include sequence type, serotype, pulsotype, phage type, and biotype.

The conserved nature of the E. Sequence typing has proved useful in many settings, e.

Escherichia coli.

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Serotyping based on antigenic variation in the surface O- polysaccharide and H- flagella antigens of E. Indeed, much of the early evidence linking EPEC to the cause of outbreaks of diarrhoea was based on the antigenic relatedness of strains obtained from patients in different locations Robins-Browne, Moreover, E. Importantly, E. Indeed, in-silico serotyping offers a number of advantages over traditional serotyping, including the non-reliance on typing sera that may vary in quality, and the ability to type strains that do not express the O- or H-antigens in vitro or that autoagglutinate Ingle et al.

For these reasons, in-silico serotyping is likely to replace traditional serotyping in future.

Nevertheless, many food microbiology laboratories currently use serotyping for the preliminary identification of EHEC, most notably E. Interestingly, even the identification of serotype, together with the demonstration of a suite of shared virulence genes, may not provide sufficiently refined information to identify a particular subclone or clade of EHEC Manning et al. In such instances, further subtyping may be required to track outbreaks.

The value of pulsotyping is exemplified by PulseNet, a surveillance network of public health laboratories that use DNA fingerprinting for the early identification of common sources of foodborne outbreaks of disease Swaminathan et al. More recently, public health laboratories have been shifting to analysis of whole genome single nucleotide polymorphisms SNPs to trace outbreaks of E.

This approach first captured the attention of the international public health community during the high-profile outbreak of diarrhoea and HUS in Germany caused by Shiga toxin producing EAEC Buchholz et al. Biotyping was once relied upon to group and separate individual strains of E. Currently, biotyping is still used to distinguish shigellae from other varieties of E. Although at present there is no comprehensive scheme to predict E.

Biochemical profiles also play a central role in the isolation and preliminary identification of E. As mentioned above, the subdivision of DEC into pathotypes has may uses. However, some isolates do not comply with the standard pathotyping scheme Table 2. Table 2. Examples of clinically significant diarrheagenic E. Hybrid strains of E.

What is perhaps more surprising is that hybrids don't occur more often. In this regard, DEC strains that infect humans seem somewhat limited in the combinations of virulence determinants that occur together, other than those that are already well characterised Table 1. A particular limitation of pathotyping concerns its limited capacity to accommodate new strains that do not comply with known categories.

These include Shiga toxin producing strains of EAEC, which some authors have assigned to a new pathotype, designated Shiga-toxin producing enteroaggregative E.

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Another problem with the current definitions of DEC pathotypes is that some strains are defined in part by negative criteria. We believe that characterising pathogens on the basis of their lack of one or more virulence determinants may group several types of distantly related or unrelated bacteria together, and cause some distinct pathogenic categories with uncharacterised virulence determinants to be overlooked. The ability to divide E. The use of sequence typing, biotyping, serotyping, and pathotyping to group similar bacteria together while separating them from others is helpful in many circumstances, such as when tracing outbreaks, but can be misleading when serotypes change or classification systems struggle to accommodate novel strains.